The present invention relates to a thermal transfer printer for recording an image on printing paper by the use of an ink sheet, and more particularly to a thermal transfer printer adapted to initialize a set of color patches (or position a 1st color ink) at start-up of printing, and an ink sheet cassette for use in the printer.
To date, there is known a thermal transfer printer designed to print a color image on printing paper by the use of an ink sheet on which different colors of ink are coated on respective predetermined areas. This type thermal transfer printer utilizes a sequential color plane printing method in which an ink sheet coated with ink corresponding to one picture for each of complementary colors to primary colors of light, i.e., yellow (Ye), magenta (Mg) and cyan (Cy), is used to sequentially print those three colors of ink on printing paper. This sequential color plate printing method requires initialization of a set of color patches immediately before start-up of printing. One conventional initializing method is described in Japanese Patent Laid-Open No. 59-143674 (1984). According to this conventional method, a bar code is provided in a space between one ink color and the other ink color on an ink sheet, and color discriminating means for sensing the color represented by the bar code is employed to sense the ink color on the ink sheet and then position a 1st color ink. Incidentally, the bar code is formed using black ink. The color discriminating means comprises an infrared sensor.
When manufacturing ink sheets, however, the above-mentioned prior art employs four colors of ink, i.e., yellow, magenta and cyan, as well as black color used for the bar code (positioning mark). Accordingly, there are needed four types of printing drums for manufacturing an ink sheet, resulting in a problem that the printing cost of the ink sheet is increased.
The foregoing prior art accompanies another problem that an ink sheet comprising only three colors of ink cannot be used in thermal transfer printers designed for an ink sheet comprising four colors, because the former ink sheet has no positioning mark.